Entropic barrier of topologically immobilized DNA in hydrogels
Entropic barrier of topologically immobilized DNA in hydrogels
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DOI：
10.1073/pnas.2106380118
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发表时间：
2021-07-13
影响因子：
11.1
通讯作者：
Muthukumar, Murugappan
中科院分区：
文献类型：
--
作者：
Chen, Kuo;Muthukumar, Murugappan
非刚性聚合物链最固有的特性是它们能够采用大量的链构象，从而产生巨大的构象熵。当这样的大分子在具有限制性空间约束的介质中移动时，它们的轨迹受到构象熵的减少。相应的自由能景观中断的熵障碍分离连续的空间域的功能作为熵陷阱，大分子可以更有利地采用其构象。大分子通过一系列熵垒的运动是限制性介质中高分子动力学的一个常见范例。然而，如果一个单链同时被许多熵陷阱捕获，最近有人提出，大分子不进行扩散，并被定位到一个拓扑挫折的动力学状态，显然违反爱因斯坦定理。使用荧光标记的DNA作为客体大分子嵌入在一个类似的带电水凝胶超过95%的水含量，我们提出了直接的证据，这种新的状态的聚合物动力学在中间的限制。此外，使用理论和实验相结合，我们测量的熵势垒为一个单一的大分子的几十个热能，这是非常长的极端亚稳性负责。这里提出的理论-实验相结合的协议是在聚合物动力学中的单分子熵垒的测定。此外，这种方法提供了一个方便的一般程序，以量化背后的单电荷大分子在拥挤的环境中的运动的普遍现象的潜在的自由能景观。
The single most intrinsic property of nonrigid polymer chains is their ability to adopt enormous numbers of chain conformations, resulting in huge conformational entropy. When such macromolecules move in media with restrictive spatial constraints, their trajectories are subjected to reductions in their conformational entropy. The corresponding free energy landscapes are interrupted by entropic barriers separating consecutive spatial domains which function as entropic traps where macromolecules can adopt their conformations more favorably. Movement of macromolecules by negotiating a sequence of entropic barriers is a common paradigm for polymer dynamics in restrictive media. However, if a single chain is simultaneously trapped by many entropic traps, it has recently been suggested that the macromolecule does not undergo diffusion and is localized into a topologically frustrated dynamical state, in apparent violation of Einstein's theorem. Using fluorescently labeled lambda-DNA as the guest macromolecule embedded inside a similarly charged hydrogel with more than 95% water content, we present direct evidence for this new state of polymer dynamics at intermediate confinements. Furthermore, using a combination of theory and experiments, we measure the entropic barrier for a single macromolecule as several tens of thermal energy, which is responsible for the extraordinarily long extreme metastability. The combined theory-experiment protocol presented here is a determination of single-molecule entropic barriers in polymer dynamics. Furthermore, this method offers a convenient general procedure to quantify the underlying free energy landscapes behind the ubiquitous phenomenon of movement of single charged macromolecules in crowded environments.